Production of unsaturated hydrocarbons by pyrolysis of saturated hydrocarbons



United States Patent C 3,336,412 PRODUCTION OF UNSATURATED HYDROCAR- BGNS BY PYROLYSIS F SATURATED HY- DROCARBONS Richard Kenneth Lyon, Elizabeth, and William Bartok,

Westfield, N.J., assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Filed June 29, 1964, Ser. No. 379,031 8 Claims. (Cl. 260-679) This invention relate to an improved process for the pyrolysis of certain saturated hydrocarbons to obtain unsaturated hydrocarbons. More particularly, this invention relates to the production of unsaturated hydrocarbons by partial combustion of saturated hydrocarbons. In a preferred embodiment, this invention relates to the production of acetylene by partial combustion of hydrocarbons such as methane.

Processes for the production of acetylene by incomplete combustion of hydrocarbons are well known in the prior art. In all these partial combustion processes the energy for the endothermic pyrolysis of the saturated hydrocarbon feed is provided by burning part of that feed with oxygen in an exothermic reaction. For example, the endothermic reaction: 2CH SC H +3H is supplied energy by burning part of the feed with oxygen in accordance with the reaction: CH +1 /zO SCO+2H O. In the commercial processes for carrying out the partial combustion of methane to produce acetylene it has been found necessary to separately preheat the methane and oxygen reactants to about 600700 C. before mixing and igniting them to produce the desired acetylene product. Such a procedure is dictated by the fact that water formed in the combustion reaction will react with acetylene at high temperatures in accordance with the reaction: 2H O+C H S2CO+3H Thus, if sufiicient oxygen were employed to obtain the amount of heat needed for the pyrolysis, significant amounts of water would be formed which, under the conditions of pyrolysis, would react with acetylene and thereby reduce the yield of desired product. The prior art partial combustion processes therefore have employed oxygen-poor reaction feeds and preheated the reactants in order to obtain the proper reaction temperature. It is obvious that such a procedure not only substantially increases the capital investment necessary for the production of acetylene but also results in increased processing costs. Furthermore, due to the nature of the above-described competing chemical reactions as well as thermodynamic considerations, the yields of the desired unsaturated hydrocarbon product from prior art commercial processes has been severely limited and in most cases has not exceeded 8%, based on the dry gas output.

It is an object of this invention to provide an improved process for preparing unsaturated hydrocarbons from saturated hydrocarbons in which a portion of the heat necessary for the reaction is supplied by the partial combustion of the hydrocarbon itself.

It is a further object of this invention to provide an improved process for the production of unsaturated hydrocarbon by partial combustion of a saturated hydrocarbon in which a portion of the heat necessary for the reaction is supplied by the partial combustion of the hydrocarbon itself and the necessity for preheating the reactants is eliminated.

Yet a further object of this invention is to provide an improved process for the production of acetylene, by partial combustion of methane, in higher yields than have heretofore been obtainable.

It has now been discovered that the yield of unsaturated hydrocarbon derivable from the partial combustion of saturated hydrocarbon can be drastically increased and that the need for preheating the reactants in the combustion reaction can be eliminated by the addition of a halogen gas to the reaction mixture. In one preferred embodiment it has now been discovered that the addition of chlorine to a mixture of methane and oxygen increases the yield of acetylene and eliminates the need for preheating the methane and oxygen reactants. While not wishing to be bound by any particular theory, it is believed that the ad dition of chlorine promotes the formation of acetylene in the reaction 3H +C 2CH by formation of HCl thereby driving the reaction in accordance with familiar principles of equilibrium reaction. Furthermore, the reaction H +Cl 2HCl is exothermic and therefore adds additional heat to the reaction. The utilization of chlorine gas with the unsaturated hydrocarbon-oxygen mixture possesses a further advantage in that the halogen gas will not react with the unsaturated hydrocarbon as will water, described above, since carbon-halogen compounds are not stable at the high reaction temperatures.

In one preferred embodiment for producing unsaturated hydrocarbons by the above-described method, the unsaturated hydrocarbon, oxygen and halogen gases are subjected to rapid intimate mixing and passed at a high linear velocity to a reaction chamber wherein the partial combustion takes place with the formation of a flame. The gases undergoing combustion are passed through the reactor at a high linear velocity so that the temperature reached during combustion is only maintained for a very short period in the range of about 0.001 to 0.1 second,

preferably 0.001 to 0.1 second. It is an essential feature v of such partial combustion reactions that the mixing and feeding of the gaseous reactants take place rapidly in such a manner that the flame reaction does not flash back and cause premature combustion in the mixing zone. Furthermore, the short reaction period is insured by providing a rapid quench zone for the hot reacted gases existing from the reaction zone. The mixing, reacting, and quenching steps of this invention may be carried out by utilizing any of the well known prior art devices which have been employed for the partial combustion of hydrocarbons.

The temperature of the flame reaction will vary between 1000 and 2000 (3., preferably 1400 and 1600" C. depending upon the nature and composition of the reactants.

A wide variety of saturated hydrocarbons may be employed in the process of this invention to produce the desired unsaturated hydrocarbons. Thus any normally gaseous or liquid cyclic or acyclic hydrocarbon can be converted into C unsaturates, predominantly acetylene, by this process. It will, of course, be necessary to prevaporize a liquid hydrocarbon feed prior to the earlier described mixing stage. Preferred saturated hydrocarbon feeds are the lighter paraffins including C to C paraflins such as propane, butane and petroleum fractions in the light naphtha range. It will be understood that the feed may constitute mixtures of the above mentioned hydrocarbons and may also contain minor amounts of other organics such as unsaturated hydrocarbons and aromatics. A particularly preferred saturated hydrocarbon feed is methane. The methane feed may be derived from natural gas which ordinarily contains methane and about 5% ethane and heavier hydrocarbons. In a preferred emcarbon will be in the range of 0.1 to 2.0. In a preferred embodiment the halogen/hydrocarbon and oxygen/hydrocarbon molar ratios are mutually adjusted to provide the optimum total amount of oxidant. Thus, when the molar ratio of oxygen to hydrocarbon is low, for example 0.05 to 0.3, the halogen/hydrocarbon range will be maintained between 1.5 and 2.0 and when employing a high ratio of oxygen near the upper limit specified above the halogen/hydrocarbon ratio will be maintained between 0.1 to 0.5. Thus, in one typical embodiment, the feed mixture to the reaction will contain 35 to 40% methane, 5 to 25% oxygen and 40 to 60% chlorine.

The invention will be further understood by reference to the following illustrative examples.

Example 1 A series of partial combustion reactions were carried out in which the ratio of methane, oxygen and chlorine in the feed composition was varied in each run. Before each experiment, the individual feed components were measured by pressure into a 3-liter mixer flask. Thorough mixing of the feed gases was insured by magnetic agita- As can be seen in the table, acetylene concentrations as high as 17-18 mole percent were achieved with rich mixtures of methane and chlorine.

The carbon mass balance was calculated by determining the ratio of the C0, C0 C H and CH products to the CH input feed. This data indicates that while some of the feed was degraded to carbon, the amounts are clearly not large. The mass balance of oxygen was calculated by the ratio of oxygen in the CO and CO products to the oxygen input. The calculated ratios indicate that very little water is formed in the product since almost all of the oxygen is consumed to form CO and CO Example 2 Experiments similar to those described in Example 1 were carried out with the exception that no chlorine was employed in the reaction mixture. Under the same experimental conditions the only mixtures which would burn were those for which O /CH was so high that no C H was formed. The results are summarized in Table 11 below.

tion of the contents of the flask. The premixed reactants were then admitted to a 5 foot long glass reactor tube having a 1.5 inch inside diameter. Thereafter, the combustion was initiated with a spark at the bottom of the glass reactor tube. The combustion wave generated moved up the tube past a pair of photo multipliers. The output of the photo multipliers was displayed on a dual-trace oscilloscope and photographed with a Polaroid camera. This procedure gave an accurate measurement of the velocity of the combustion wave and the nature of its light output thereby making it possible to determine the reaction time. After combustion, the product gases were transferred by means of a vacuum sampling arrangement to a pair of gas chromatographs equipped with thermal conductivity type detectors in series. The first detector measured C H C H and CO content in the product gas by employing a silica gel column. The second detector employed a molecular sieve column and determined the concentrations of the CO, CH; and 0 product components. HCl, C1 and H 0 were not capable of being detected in this gas chromatograph procedure. The composition of the output gases in each run was calculated on a dry gas basis and did not include H O, HCl or the traces of air which the sample may have picked up during handling. The results are tabulated in Table I below:

These results indicate that partial combustion in the absence of a halogen promoter is distinctly inferior to the process described in this invention since it does not result in the formation of unsaturated hydrocarbon.

As previously described in this specification, the major reaction products of the above described partial combustion of CH, are C H C0, C0 and HCl. This reaction product may be further treated by a variety of techniques in order to recover selected components or alternatively subjected to further reaction for the purpose of producing valuable unsaturated compounds from acetylene. For example, the HCl can be easily separated from the reac tion mixture by absorption in water and subsequently be oxidized to produce chlorine which may be recycled to the partial combustion reaction. Alternatively, without removal of the CO and CO products the mixture of acetylene and hydrogen chloride, CO, and CO may be reacted employing well known prior art techniques to produce vinyl chloride. Vinyl chloride is easily removed from C0 and CO by condensation or solvent extraction.

The partial combustion reaction product of this invention may also be treated by passing the entire product gas over a nickel catalyst in the presence of steam. The water gas shift will produce hydrogen and the hydrogen may then hydrogenate the acetylene to ethylene. Under proper steam/hydrocarbon ratios and with the proper residence times a nickel catalyst may be used to carry out the water gas shift and hydrogenation steps in a single operation. The ethylene produced can be passed over a suitable polymerization catalyst, such as phosphoric acid on Kieselguhr, to produce hydrocarbon products boiling in the gasoline range. Thus, the over-all process of this invention may be visualized as the upgrading of methane into gasoline or other higher molecular weight or valuable hydrocarbon products.

Having thus described the general nature and the specific embodiments of the invention, the true scope will now be pointed out by the appended claims.

What is claimed is:

1. A process for forming C unsaturated hydrocarbons which consists essentially of pyrolyzing a mixture of a C -C saturated hydrocarbon, oxygen and a halogen selected from the group consisting of chlorine and bromine at a temperature in the range of 1000 to 2000 C. for a period of 0.001 to 0.1 second.

2. The process of claim 1 wherein the molar ratio of oxygen to hydrocarbon is in the range of 0.05 to 0.6 and the molar ratio of halogen to hydrocarbon is in the range of 0.1 to 2.0.

3. The process of claim 2 wherein the halogen is chlorine.

4. A process for producing acetylene which consists essentially of pyrolyzing a reaction mixture comprising methane, oxygen and a halogen selected from the group consisting of bromine and chlorine at a temperature in the range of 1000 to 2000 C. for a time in the range of 0.001 to 0.1 second.

5. The process of claim 4 wherein the molar ratio of oxygen to hydrocarbon is in the range of 0.05 to 0.6 and 6 the molar ratio of halogen to hydrocarbon is inthe range of 0.1 to 2.0.

6. The process of claim 5 wherein said halogen is chlorine.

7. The process of claim 4 wherein the pyrolyzed mixture is quenched subsequent to said pyrolysis.

8. A process for producing acetylene which comprises pyrolyzing a reaction mixture comprising to mole percent methane, 5 to 25 mole percent oxygen and 40 to mole percent chlorine at a temperature in the range of 1000 to 2000 C. for a time in the range of 0.001 to 0.1 second, quenching the pyrolyzed reaction mixture and recovering said acetylene.

References Cited UNITED STATES PATENTS 3,205,280 9/1965 Wattimena et a1. 260-679 DELBERT E. GANTZ, Primary Examiner.

ALPHONSO D. SULLIVAN, Exmainer.

G. E. SCHMITKONS, Assistant Examiner. 

1. A PROCESS FOR FORMING C2 UNSATURATED HYDROCARBONS WHICH CONSISTS ESSENTIALLY OF PYROLYZING A MIXTURE OF A C1-C6 SATURATED HYDROCARBON, OXYGEN AND A HALOGEN SELECTED FROM THE GROUP CONSISTING OF CHLORINE AND BROMINE AT A TEMPERATURE IN THE RANGE OF 1000* TO 2000*C. FOR A PERIOD OF 0.001 TO 0.1 SECOND. 